1. Field of the Invention
The invention relates to crystallographic models and more particularly to models of crystal structure having movable tangent spheres whose X,Y coordinates are defined by vertical rods passing through the spheres into a base.
2. Prior Art
Numerous devices incorporating spheres to represent atoms, ions or molecules have been developed and utilized to illustrate the sequence and spatial relationships of atoms, ions or molecules in a crystal structure. Such devices have been, in whole or in part, the subject of books, bibliographic monographs, surveys, patents, commercial development, as well as numerous individual articles appearing in the technical and educational literature of the physical sciences.
Perhaps the most comprehensive bibliography of materials on crystal models is contained in the publication entitled "Bibliography on Molecular and Crystal Structure Models" by Deane K. Smith, National Bureau of Standards Monograph 14, U.S. Department of Commerce, 1960.
According to the "open" and "closed" classifications of these crystal structure devices as set forth by Smith, the various types are briefly summarized as follows.
Open models are those with spheres, representing crystal structure lattice site occupants, not touching. The following are different types: (a) ball and spoke of the type having spheres, with receptor sites, joined by rod like connectors of various lengths at various angles; (b) ball and shelf of the type having spheres nested in smaller recesses of fixed plates, the plates corresponding to crystal structure planes; (c) ball and vertical rod of the type having vertical rods, with spheres at fixed or adjustable heights, mounted in a base; (d) ball and polyhedron of the type having parts of spheres adhesively secured at various positions on a hollow polyhedron made of joined transparent thin polygons.
Closed packing models are those with spheres, representing crystal structure lattice site occupants, touching. The following are different types: (a) pyramid stacking of the type having a horizontal base layer of spheres confined by various methods, with subsequent layers of spheres stacked via nesting on preceding layers; (b) container stacking of the type having spheres packed inside of a transparent hollow polyhedron; (c) ball and spoke of the type like ball and spoke open models except rod like connectors are shortened; (d) ball and shelf of the type like ball and shelf open models except horizontal plate separation is designed to effect tangency of spheres; (e) contact binding in which spheres are permanently joined at contact points by various adhesive techniques; (f) ball and vertical rod of the type like ball and vertical rod open models except spheres are tangent.
In closed models, spheres are usually held in place in such a manner as to prevent visual access to the interior portion. In open models interatomic distances and symmetry are more clearly illustrated by spheres which are also held in place.
It is an object of the present invention to provide a crystal model which has the main advantages of both open and closed models. Such a model would illustrate the close packing of tangent spheres of identical as well as different radii, characteristic of closed models, while illustrating interatomic distances, symmetry and spatial relationships, in general, of open models in a clear manner. The spatial relationships to be illustrated include the unit cell concept, simple lattice types, ion sizes, the coordination number concept, cation-anion relationships (interlocking lattices) and layer structures as well as stoichiometric relationships.